This invention relates to plastic compositions containing a photosensitizer which renders the composition degradable by ultraviolet radiation.
The advent of plastics has given rise to improved methods of packaging goods. For example, polyethylene and polypropylene plastic films, bags, bottles, styrofoam cups and blister packages have the advantages of being chemically resistant, relatively unbreakable, light in weight and translucent or transparent. The increasing use of plastics in packaging applications has created a serious waste disposal problem Burning of these plastic materials is unsatisfactory since it adds to air pollution problems.
Unlike some other packaging materials, such as paper and cardboard, plastics are not readily destroyed by the elements of nature. Thus, burying them is not an effective means of disposal, and can be expensive.
Plastics are biologically recent developments, and hence are not easily degradable by micro-organisms which attack most other forms of organic matter and return them to the biological life cycle. It has been estimated that it may take millions of years for organisms to evolve which are capable of performing this function. In the meantime, plastic containers and packaging films are beginning to litter the countryside after being discarded by careless individuals.
One means suggested for combating the plastic waste disposal problem has been the use of plastic compositions which degrade upon exposure to ultraviolet light. Plastics are made up of large molecules, the atoms of which are linked together to form chains. It has been suggested to introduce a "sensitizer group" along the polymer chain which would absorb the ultraviolet light of the sun and, using this energy, break the polymer chain. When the chains are broken, the plastic loses its physical strength and becomes brittle, so that it is easily broken apart by natural erosion of the wind, waves, or rain into small particles which become part of the soil.
The sensitizer groups in previously known compositions, are chemically bonded to other atoms in the polymer chain. The introduction of these sensitizer groups into the polymer chain can be complicated, and requires precise control in order to obtain the proper sensitizer concentration. Thus, there has been a need for a plastic composition degradable by ultraviolet light which can more easily be prepared.